In vivo and in vitro immunologic cross-reactivity between SV40 virus transformed prostatic tissue and fetal antigens of a syngeneic strain of hamsters (SLH) suggests a similarity between fetal antigens and tumor-associated antigen of prostatic tissue transformed by a DNA oncogenic virus. Attempts were made to isolate and characterize these oncofetal antigens. An immunogenic murine bladder tumor has been developed to study the various techniques for immunotherapy of bladder cancer. The consistency of tumor induction, its natural history, and its immunogenicity both in vivo and in vitro render this murine bladder tumor a suitable model for immunologic studies. We are attempting to isolate the tumor-associated antigen of this chemically-induced murine bladder tumor.